JPS63961Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a small-sized turbine overspeed prevention device that mainly uses a low boiling point medium as a working fluid.

Waste heat energy such as process exhaust gas and heated wastewater discharged from chemical plants, steel plants, thermal or nuclear power plants, thermal energy obtained from the natural world such as solar heat, geothermal heat, ocean temperature difference, LNG,
In order to effectively utilize the cold energy possessed by LPG and other sources, power generation plants are in the practical stage that drive small turbines using low boiling point media such as chlorofluorocarbons, butane, and ammonia in a Rankine cycle configuration as the working fluid. A typical configuration of this power plant is shown in Figure 1.

First, we will explain the cycle by using seawater as a high heat source, such as the above-mentioned waste heat energy, and as a low heat source, using the cold energy possessed by LNG and LPG.
Seawater 1 is led to an evaporator 2 by a pump, and after giving heat to a low boiling point medium to evaporate it, it is discharged outside the system or returned to the sea. The low boiling point medium steam generated in the evaporator 2 is guided as the working fluid of the system to the turbine 5 via the main steam stop valve 3 and the steam control valve 4, where the thermal energy is converted into rotational energy, and the thermal energy is converted to rotational energy. Recovered as electrical energy. The working fluid that has been expanded and finished its work in the turbine 5 is led to the condenser 7. In condenser 7, LNG,
The working fluid is liquefied by heat exchange with the cold heat of the LNG and LPG pumped from the LPG storage tank 8 by the pump 9, and this liquefied working fluid is pressurized by the boost pump 10 and returned to the evaporator 2. be done.
This constitutes the so-called Rankine cycle. Condenser 7
On the other hand, the LNG and LPG gases vaporized in the evaporator 11 further absorb heat from the seawater 1 and evaporate.
Air is supplied to processes such as factories.

Naturally, the steam turbine 5, which is the prime mover of such a cycle, is also subject to the ``Technical Standards for Thermal Power Plants for Power Generation,'' and its speed governor is ``an emergency governor that determines the speed reached when the rated load is cut off.'' The speed at which the emergency governor operates must be 111% or less of the rated speed.

The instantaneous maximum speed after the load rejection is calculated by the following known formula:

However, C = constant E _R = rotational energy at rated rotation △E ₁ = energy flowing into the turbine with respect to the valve delay time after load cutoff (the valve is steam control valve 4 in Figure 1) △E ₂ = load After shutoff, the energy flowing into the turbine for the valve closing time (the valve is a steam control valve in Figure 1) △E ₃ = Energy in the turbine and steam pipe at the time of load shutoff and used to increase speed GD ² = Turbine, Moment of inertia of the rotating part of the generator Generally speaking, this type of power generation plant is not installed for the purpose of supplying power to the power grid, but rather for the purpose of effectively utilizing waste heat energy and energy possessed by nature. Since the steam turbine 5 and generator 6 are small and their output is relatively small, it is thought that the maximum speed after load shedding can be kept low compared to a general thermal steam turbine. ) The specific volume of the low boiling point medium is very small, so the steam passage area required to flow a certain amount of steam is small. For this reason, the turbine nozzle, blades, etc. are also smaller, and the moment of inertia of the rotating parts of the turbine and generator is also smaller.

(2) The smaller the valve delay time and valve closing time, which are the main factors that determine the maximum speed after load shedding, the smaller the maximum speed, but it is not necessarily proportional to the steam turbine and generator capacity. It is not shortened, but there is a certain amount of signal transmission delay to the valve, and there is an operation limit speed due to the valve hydraulic drive mechanism.

For the above reasons, it can be said that the instantaneous maximum speed of a steam turbine using a low boiling point medium is extremely high.

In order to solve the above-mentioned problems with small turbines that use low-boiling point media as the working fluid, this invention supplements the current turbine speed governor and can suppress the instantaneous maximum speed below the specified value. Provides an overspeed prevention device.

First, the basic points of interest of this invention are as follows.
In the conventional technology, in order to suppress the instantaneous maximum speed of the steam turbine, △E ₁ and △
E ₂ decreases energy. In other words, in order to shorten the valve delay time and valve closure time after load interruption, the signal transmission method to the valve should be changed from mechanical to electrical, or the working medium of the valve drive mechanism should be changed from low-pressure oil to high-pressure oil. We have been working on increasing the operating speed. However, since there is a limit as mentioned above, the present invention attempts to reduce the ΔE ₃ energy in equation (1).

ΔE ₃ energy is the energy generated when the steam present in the turbine and steam pipes expands into the condenser at a lower pressure and energy level, and the rate of expansion is influenced by the differential pressure. The detailed mathematical expression is as follows.

△E ₃ ∝V/v×(i ₁ −i ₂ )×η …(2) V: Volume inside the turbine and steam pipe (shown with diagonal lines in Figure 2) v: Specific volume of steam i ₁ − i ₂ ; Turbine and Difference η between the energy of the steam in the steam pipe (enthalpy i ₁ ) and the energy in the condenser (enthalpy i ₂ ); rate at which the steam in the turbine and steam pipe expands to the internal pressure of the condenser Among these elements, V is the structure Above, v, (i ₁ −
i ₂ ), η is determined by the operating conditions at the time, but the expansion ratio coefficient η is the differential pressure between the steam pressure P ₁ in the turbine and steam pipe and the pressure P ₂ in the condenser △P = P ₁ − R ₂
is a function η=f(ΔP) whose factor is η=f(ΔP), and its characteristic curve is shown in FIG. When the differential pressure △P decreases, η
will also decrease.

From the above, in this invention, the pressure in the turbine exhaust chamber is forcibly increased during load interruption, and the differential pressure △P, that is, the expansion rate is reduced, thereby reducing the energy △E ₃ used to increase the speed in the turbine and steam pipe. The purpose is to suppress the instantaneous maximum speed as a result.

This will be explained in detail in the figures below.

In the description of the embodiments of the present invention, members that are the same as those in the prior art are designated by the same reference numerals, and the description thereof will be omitted.

FIG. 4 shows an embodiment of the present invention, in which a control butterfly valve 12 is installed in the middle of an exhaust pipe 11 connecting a turbine exhaust chamber and a condenser. FIG. 5 is a detailed diagram including the drive mechanism. FIG. 6 shows another embodiment, in which a valve 13 having a check valve structure is installed in the middle of the exhaust pipe. FIG. 7 is an ON-OFF operation block diagram of the device for increasing exhaust pressure during load interruption.

In FIG. 7, the signals sent to the signal receiving section 12a of the exhaust pressure increasing device A are composed of a turbine load cutoff signal 14, a turbine trip signal 15, a turbine rotation speed increase signal 16, and a turbine rotation speed decrease signal 17. be done. These signals are input to the OR circuit 18 when a turbine load shedding or turbine trip occurs. The turbine rotational speed increase rate signal 16 is a signal generated when the rotational speed increase rate exceeds a certain value (a sudden increase in rotational speed occurs during turbine load shedding or tripping), and is similar to the load shedding signal 14 and tripping. It has a backup element of signal 15. The signal of this OR circuit 18 becomes the input signal of the turbine rotational speed decreasing signal 17 and the AND circuit 20, and when the turbine rotational speed does not decrease, the condition is met and the signal receiving part of the exhaust pressure increasing device A is turned on.
A movement is emitted.

The temperature in the low-pressure exhaust chamber of this type of turbine is generally lowered to about a minus number plus, and the exhaust pressure increase device A operates to increase the exhaust pressure, and the turbine blades It is thought that a rapid temperature rise due to frictional heat will not occur even when the turbine rotates (by the way, thermal power steam turbines are normally operated at around 400℃, and in such cases, an additional temperature increase of several tens to 100 degrees will occur instantaneously). ). In addition, when the rotation speed of the exhaust pressure increasing device A exceeds the peak value and enters a descending state, the turbine descending signal 17 is established.
The operation is stopped upon receiving an OFF signal from the AND circuit 20, but the operation time during that time is only a few seconds, which also serves as a factor in preventing a sudden rise in temperature.

On the other hand, what must be taken into consideration is the increase in turbine shaft vibration due to a sudden increase in exhaust pressure.
This can be suppressed by using a valve or a devised valve as described below to reduce the rate of increase in exhaust pressure. Signals 15 and 16 indicate that there is no possibility that the instantaneous maximum speed will reach the specified value not only in the low load region but also when the turbine load is cut off or when the turbine is tripped.
There is no need to input it, only when the load is greater than the pre-calculated load.

Returning to FIGS. 4 and 5, such a turbine exhaust pipe 11 has a relatively small diameter, and it is not difficult to install a control valve such as a butterfly valve 12 in the middle of the pipe. During normal operation, the butterfly valve 12 maintains its position along the steam flow within the exhaust pipe 11 (solid line in FIG. 5). When the exhaust gas raising device A receives the ON signal at the signal portion 12a as described above, it operates in the direction of closing the butterfly valve 12 via the lever and link mechanism 12b (broken line in FIG. 5).
Furthermore, even in the fully closed position (dashed line in Figure 5), this butterfly valve 12 does not completely block the flow path and allows a predetermined amount of working fluid to pass through, thereby preventing a sudden pressure rise and preventing the final stage of the turbine from closing. It is designed to prevent abnormal forces from acting on the wings. For this reason, the steam flowing from the turbine exhaust chamber is subjected to resistance, which inevitably increases the pressure in front of the valve. As mentioned above, this reduces the expansion rate coefficient η,
This will reduce the energy used to increase speed. The controllability required of this butterfly valve 12 is not steam flow rate control or condenser internal pressure control, but a simple one that temporarily provides resistance to the flow, and the drive unit suitable for this is also a simple mechanism. is sufficient. In addition, in Fig. 6, when receiving the ON operation signal in the same way as above, the valve moves to the position shown by the broken line, provides resistance to the steam flow, and reduces the differential pressure between the turbine or steam pipe internal pressure and the exhaust side pressure. This will reduce the expansion rate, that is, the energy △E ₃ used to increase the speed. Check valve 1 in the diagram
The through hole 13a provided in the center of the valve body 3 prevents a sudden pressure rise and prevents abnormal force from acting on the final stage blade of the turbine.

As explained above, the small turbine overspeed prevention device of the present invention assists the current speed governor at a relatively low cost and suppresses the instantaneous maximum speed of a small turbine at load cutoff to below a specified value. According to the present invention, since the valve is formed so that a predetermined amount of working fluid can pass through even in the fully closed position, a sudden pressure increase in the turbine exhaust chamber pressure is prevented, and the turbine No abnormal force is applied to the final stage blade.

Further, the valve closes when any one of the turbine trip signal, load shedding signal, or rotation speed increase signal is output, but the rotation speed decrease signal is not output even if each of the above signals is output. Since the valve is configured to open when the turbine speed decreases, the valve will not be closed for a long time after the rotational speed of the turbine has decreased, and an abnormal rise in temperature in the turbine exhaust chamber can be prevented.

[Brief explanation of drawings]

Figure 1 is a typical system diagram of a power generation plant that uses a low boiling point medium as the working fluid, Figure 2 is an explanatory system diagram that explains the energy used to increase speed in the turbine and steam pipe during load shedding, and Figure 3 is an explanatory diagram of η representing the degree of expansion of the steam in the turbine and steam pipe, FIG. 4 is a system diagram showing one embodiment of the device of the present invention, FIG. 5 is a longitudinal cross-sectional side view of the turbine exhaust pipe, and FIG. A vertical cross-sectional side view of a part of the turbine exhaust pipe showing another embodiment of the invention, FIG. 7 is an ON view of the device of the invention.
-OFF signal operation block diagram. 5... Turbine, 6... Generator, 7... Condenser, 11... Turbine exhaust pipe, 12... Butterfly valve, 13... Check valve, A... Exhaust pressure increasing device,
14...Load cutoff signal, 15...Turbine trip signal, 16...Turbine rotation speed increase rate signal, 1
7...Turbine rotation speed decrease signal.

Claims (1)

[Scope of utility model registration request] In a turbine overspeed prevention device, a valve is provided in the middle of an exhaust pipe leading from a turbine exhaust chamber to a condenser, and the valve is closed to increase the exhaust pressure in the turbine exhaust chamber. , a valve that can allow a predetermined amount of working fluid to pass through even in the fully closed position, and an exhaust pressure increase device that can open and close this valve. The valve is configured to close when any one of the rotation speed increase rate signals is output, and to open the valve when a rotation speed decrease signal is output even if any one of the signals is output. Turbine overspeed prevention device.